The present invention relates to a printer provided with a unit for forming an image and an endless intermediate belt trained under tension around rollers in such manner that the belt can rotate over the rollers, the intermediate belt being operatively connected to the image forming unit for transfer of the image from the image forming unit to a receiving material, wherein the intermediate belt comprises a fabric of threads as a support.
A printer of this kind is known from European Patent EP 0 671 671 B1. The image-forming unit of this printer comprises an endless photoconductor on which an image of toner particles can be formed by successively charging the photoconductor, exposing it image-wise and developing the resulting latent image with toner. This image is then transferred in a first transfer step to an endless intermediate belt. This belt consists of a polyester fabric provided with a 2 mm thick silicone rubber top layer. The belt is trained under tension around a number of rollers, one of which serves as a drive roller. Using the drive roller, the belt can be rotated over the rollers so that the image can be transported to a subsequent transfer location. Here the belt is brought into contact with a receiving material, the image being transferred under the influence of temperature and pressure from the belt to the receiving material. Any residues of the image on the intermediate belt are removed by means of one or more cleaning rollers.
One disadvantage of this known printer is that there is always a certain loss of image register because of the transport of the image by the intermediate belt. In other words, it is never entirely certain where the image will finally arrive on the receiving material. In addition, there will always be some degree of image distortion, for example deformation of a straight line to a somewhat curved line. The reason for this is not completely clear but it is known that the problems can be reduced by using a belt control mechanism. Known belt control mechanisms are, for example, passive mechanisms such as flanges, by means of which any deviation of the belt in the axial direction, i.e. the direction parallel to the roller axes, is limited, or the use of rollers which are self-controlling. Using such rollers which are, for example, somewhat bevelled at the ends, it has been found that the belt stays within certain limits. Active belt control mechanisms often use a roller in which the position of the axis can be changed. By a slight change of this position the belt can actively be controlled in the axial direction.
These known belt control mechanisms solve the above-mentioned problems only to a restricted degree. In addition, each of the above-mentioned mechanisms has additional disadvantages. Flanges against which a belt runs may damage the belt. Self-controlling rollers have only a restricted working area and active control mechanisms require complex measuring and regulating mechanisms and are hence relatively expensive, and in addition they do not solve the problem of image distortion.